1. Field of the Invention
The present invention relates generally to an apparatus and a method for transmitting power, and more particularly, to an apparatus and a method for transmitting wireless power by using a resonant coupling.
2. Description of the Related Art
A wireless power charging technology is currently being used for numerous electronic devices, such as an electric toothbrush, an electric shaver, a mobile phone, and a digital camera. Extensive research is currently being conducted on wireless charging of a large size battery for an electric car and a subway.
The wireless power charging technology generally includes a magnetic field inductive coupling type, which is most popular, an electric field capacitive coupling type, and a Radio Frequency (RF) wave radiation type.
The inductive coupling type has the same principle as that of a transformer, whereby resonant frequencies of the primary coil and the secondary coil are matched with an operating frequency of a power source. Increasing a wireless power transmission distance by increasing a Q factor of each coil is defined as the resonant coupling type. The primary coil is referred to as a transmission resonator and the secondary coil is referred to as a reception resonator.
Data communication between a Tx resonator and an Rx resonator is performed to efficiently charge power in the wireless power charging system. For example, authentication information between the transmitter and the receiver, information on a charged voltage or current, and information on an abnormal state of the receiver are transmitted through a data communication scheme such as in-band communication using a carrier frequency band of wireless power and out-band communication using a separate band (for example, 2.4 GHz Zigbee®).
In the wireless power charging technology using inductive coupling, a coupling efficiency between the Tx coil and the Rx coil is important, and a high power charging efficiency can be acquired when the Tx coil and the Rx coil are adjacent to each other.
The wireless power charging technology using conventional inductive coupling arranges the Tx and the Rx coil by using a permanent magnet or an electric motor. Alternatively, the wireless power charging technology places the Tx coil in an array type, selects the Tx coil closest to the Rx coil when a terminal having the Rx coil approaches, and transmits wireless power to the Rx coil through the selected Tx coil.
FIGS. 1A to 1F illustrate examples of a wireless power charging using the conventional induction coupling type.
FIG. 1A illustrates a transmitter, that is, a charging pad, and FIG. 1B illustrates a receiver, that is, a mobile terminal.
FIG. 1C illustrates a correct example of wirelessly charging power, and FIGS. 1D to 1F illustrate incorrect examples of wirelessly charging power. A transmitter 110 has a coil 111 installed therein and a receiver 120 has a coil 112 installed therein. In order to wirelessly charge power by using the inductive coupling type, positions of the coils of the transmitter and the receiver should be the same as illustrated in FIG. 1C. When coil arrangement states of the transmitter and the receiver are good, efficient wireless power transmission is possible. However, FIGS. 1D to 1F illustrate examples where coil arrangement states of the Tx coil of the transmitter and the Rx coil of the receiver are not good, which results in poor wireless power transmission.
The wireless power charging technology basically requires accurate arrangements of the Tx coil and the Rx coil and has a problem in that a size of the Tx coil and a size of the Rx coil should be almost the same. The Rx coil is located in a main body of a tablet Personal Computer (PC), but internal components of the main body of the tablet PC may prevent the Rx coil from being located in the center thereof. In this case, there is a limitation in the arrangements of the Tx coil and the Rx coil. For example, when the tablet PC is placed on the wireless charging pad, if the tablet PC is placed with a rotation of 90 degrees or placed in such a manner that a part of a main body of the tablet PC is not in contact with the wireless charging pad, arrangement states of the Tx coil within the wireless charging pad and the Rx coil within the tablet PC are not good, thereby rapidly decreasing the efficiency and stopping the wireless power transmission.